The invention relates to an arrangement for processing the projecting spine of a book block suspended from a circulating clamp on a bookbinding machine. The arrangement comprises a processing device that faces the book block spine and is installed opposite the clamp on the conveyor, as well as a corresponding tensioning device that acts perpendicularly on the clamp and the overhanging portion of the book block from both sides. The tensioning device includes a locally fixed support roller and an adjustable pressing roller.
Arrangements of the aforementioned type are used for processing the spines of book blocks in bookbinding machines used for further print processing. In the process, printed sheets or signatures are collected ahead of time in a collating machine and combined into loose book blocks. The loose book blocks are then transferred with their spines pointing downward to the clamps of a circulating conveyor on the bookbinding machine, and are clamped in. The book blocks, which are suspended in the clamps, are then moved past processing devices arranged along the conveying path. The processing devices process the spine and the adjacent side flanks of the book blocks. The clamps must exert a sufficient clamping force onto the book blocks to safely absorb the forces acting upon the book blocks during processing, and/or to prevent displacement of the book blocks inside the clamps. The minimum required clamping force depends on the type of processing, and the consistency of the book blocks. The minimum required clamping force is primarily low along the conveying path. However, one exception is the spine-processing station, which requires a high clamping force since the book blocks could otherwise be pulled from the clamp during the processing.
It has proven useful to have the clamps themselves exert a low clamping force, and to provide an additional, supporting force in the spine processing region. The additional supporting force acts from the outside upon the clamps. According to prior art, this additional force is exerted onto the clamps in the spine processing region by two rollers that the clamp moves between. The pressing roller acting upon the adjustable clamping jaw in the front is spring-loaded. The support roller acting upon the rear clamping jaw is fixed to the machine frame. The additional force to be exerted onto the clamp can be adjusted by adjusting the pre-tensioning of the spring. The distance between the pressing roller and the support roller can furthermore be selected, so as to adjust to the book thickness. As a result of the linear spring rate for the spring-loading of the pressing roller, small thickness differences between the book blocks do not cause substantial changes in the additional force. The position of the pressing roller, however, changes corresponding to the thickness differences. It has turned out that with larger thickness differences for the book blocks, such as are encountered when producing printed products according to client profiles, the dynamic forces become excessively high as a result of the acceleration and delay of the pressing roller transverse to the clamp, and the force required for the processing can no longer be ensured. In addition, with larger thickness differences, the clamps and rollers are subjected to increased stress, which can result in additional wear and tear. This effect is further increased with perfect binders operating at high production speeds.